Shrinking Behaviour of Badland Soil Under Different Soil Covers

Indicators used to estimate the soil structure stability facing erosion are the basis of major indicators of soil quality, and their behaviour is affected by permanent soil properties, vegetation and management. The relation between the pore-volume fraction occupied by water and the pore size distribution in clay soils is studied by the shrinkage curve describing clay soil porosity dynamics as a function of soil moisture. The aim of this work is to study the shrinking behaviour of the surface soil in a badland site through the shrinkage curve and to assess its relations with vegetation. Six treatments with different soil vegetation cover and aspect were selected on a badland site in Pisticci (Southern Italy). Shrinkage curves were built from natural aggregates collected in the 0-10 cm soil depth. Soil stability under shaking in water was also determined, with pre-treatments in water, alcohol and benzene for the determination of the SSI (Soil Stability Index). Soil organic matter, electrical conductivity, ESP were determined in order to investigate the relations between soil cover, chemical properties, SSI and shrink-swell behaviour. Vegetation was associated with lower soil salinity and ESP, and higher soil organic matter content. Vegetated sites showed a higher SSI and a lower overall swelling. The shrinkage curves for samples from vegetated areas lack of the structural phase of shrinkage, likely due to the combined effect of lower ESP and the mechanical effect of plant roots. All soil properties and indicators point to a higher stability of soils under grass in the south aspect and under shrub in the north one.